The present invention relates to an internal-combustion engine with a carburetor. More particularly, the present invention relates to an engine with a diaphragm carburetor which, in order to form a starting and control device, is provided with an additional drilled injection passage which communicates with the fuel line via a flow-controllable feed line.
Internal-combustion engines have been known for a long time in many areas of application and, more particularly, for use in power chain saws. For the operation of an internal-combustion engine it is necessary to supply air and fuel at a specific ratio for each operating level, depending upon rotational speed and load. The function of the carburetor is to apportion the correct amount of fuel to the air drawn in and to effect the proportioning of the volume of the air-fuel mixture necessary for adjusting the operating level. This preparation and supplying of the internal-combustion engine with an appropriate fuel-air mixture is, for the most part, possible to carry out without any difficulties during the operation of the internal-combustion engine.
For the cold start or the dry start, i.e., the start subsequent to the carburetor having dried out in an internal-combustion engine which has previously been strongly heated, starting devices are required. Such devices provide a very rich fuel-air mixture since, in order to compensate for the poor evaporation under cold start conditions, an increased amount of fuel must be supplied to the internal-combustion engine until it starts running. In addition, the starting devices enrich the mixture to the necessary extent until the normal operating temperature of the internal-combustion engine is reached.
Typical starting devices are constructed in the form of choke valve starters, in which, in order to bring about the start, the choke located before the Venturi tube is closed and, at the same time, the throttle flap is opened a little. The reduced induction pipe pressure then acts upon the main jet system and it supplies the additionally necessary fuel.
The use of such a choke system is subject to difficulties particularly when a diaphragm pump acted upon by pressure pulses is used as a fuel pump which, in turn, is acted upon by the power surges in the crankcase of, for example, a two-stroke engine. Due to the closing of the choke, a pressure equilibrium is established in each case between the fuel pump, the fuel flow area and the intake area communicating with the cylinder in such a way that the flow of fuel does not begin or begins only to a very limited degree. In internal-combustion engines intended to be started with the aid of manually actuated starting devices, this results in a considerable starting effort which reduces the handling comfort of such an internal-combustion engine.
Moreover, the choke mounted in the intake portion, during the normal operation of the internal-combustion engine, i.e., subsequent to the starting phase, develops a significant flow resistance. This flow resistance leads to substantial compromises in the carburetor design and the ensuing disadvantages cannot be completely eliminated. Thus, for instance, it is not possible to completely eliminate the additional turbulence of the air entering through the choke.
It would be advantageous to construct the internal-combustion engine and/or the carburetor in such a way that it would be possible to carry out a cold start or a dry start without requiring a choke.
Especially when diaphragm carburetors are employed, such as in power chain saws, control malfunctions frequently occur. Thus, at high carburetor temperatures, e.g., above 50.degree. C., problems arise in the fuel supply. These problems or malfunctions are, as a rule, caused by evaporating fuel since the vaporous fuel, on the fuel side, presses upon the regulating diaphragm, whereby the control valve, which is generally constructed in the form of a needle valve, is closed. At temperatures ranging from 25.degree. C. to 30.degree. C., for instance, the carburetor on a power chain saw is, in operation, heated to approximately 65.degree. C. within a period of approximately 10 minutes.
When such a heating of the carburetor takes place and, with it, of the entire fuel conveyance routes, a substantial evaporation of fuel then occurs such that a starting of the engine is no longer possible. An enforced cooling interval of at least 20 minutes is then required. Thus, the utilization possibilities of chain saws, particularly in summer, are severely restricted, especially since it is impossible to make provision for such a chain saw to remain in uninterrupted operation. The existing possibility of keeping the internal-combustion engine of the power chain saw operative in the interval periods at idling speeds is no longer acceptable for reasons related to environmental protection, such as exhaust gas annoyance, noise nuisance, and waste of energy.
An increased spatial separation of the carburetor from the cylinder head of the internal-combustion engine results in disadvantages due to the correspondingly longer flow paths.
Prior solutions to this problem have been to provide a more substantial heat insulation between the carburetor and the cylinder of the internal-combustion engine. However, this solution is subject to the disadvantage that, at colder temperatures when a heating of the carburetor by the cylinder of the internal-combustion engine is desired, icing up of the carburetor takes place.
In order to solve the problems to which attention has been drawn in the foregoing, more particularly the problem of the cold start, prior art solutions have also been proposed which fit an additional manual primer to the carburetor. However, the structural and space-related effort connected herewith has proved to a disadvantage. Further, this solution, too, has so far not led to the desired results since a formation of vapor bubbles could not be prevented by this. Moreover, with a primer, an adjustment is no longer possible once the internal-combustion engine has started running. Also, an exact apportionment of fuel is not feasible by this means so that the problem of the engine becoming flooded is ever-present.
Due to the foregoing considerations, an internal-combustion engine of the type stated in the beginning has already been proposed; (see, for example, German Patent Number DE-GM 87 10 075). Tank recirculation devices are also already known.
However, it is the object of the present invention to further develop an internal-combustion engine in such a way that additional priming under all starting and environmental condition results in a start without any difficulties.
This technical problem is solved by the features embodied in the present invention.